When asked to identify a structure that affected their ability to communicate, most firefighters may properly include their dispatch center or a tower site. While these would be appropriate responses, because these facilities provide significant support to the radio system, attention must also be...
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When asked to identify a structure that affected their ability to communicate, most firefighters may properly include their dispatch center or a tower site. While these would be appropriate responses, because these facilities provide significant support to the radio system, attention must also be given to those buildings that have a negative effect.
Although not often considered in this light, the reduction of communications capacities caused by the design and materials of some buildings can be as deadly to firefighters as an overloaded lightweight truss. While the presence of the latter may not be readily known without a vigorous pre-plan inspection, so too may hidden radio dead spots evade detection without some firsthand knowledge of the structure involved. In either case, failure can prove costly.
Because radio waves are invisible, it is sometimes difficult to comprehend how they work, let alone what can keep them from working. Exploring the issue from a fire service perspective, we can look at the flow of electrons in a radio wave much the same way we look at the flow of water. If there is no obstruction in the hose between the pump and the fire, and if there is sufficient pressure to overcome the friction loss, the attack crew will have a viable stream. Similarly, if there is no "kink in the line" between the transmitter and the fireground, and the signal is strong enough to overcome the electronic friction loss created by man-made and natural phenomena, two-way communication will be possible.
Just as water flow can be impacted by a variety of factors such as hose diameter, elevation, and the number and condition of the fittings used in the evolution, many factors can hamper effective radio transmissions. In lower frequencies, atmospheric conditions can create a condition known as "skip," whereby calls made in one jurisdiction bounce along the atmosphere, often to be heard more clearly hundreds of miles away than they are just around the corner. On the other end of the spectrum, higher frequencies can be adversely affected by heavy foliage, meaning that a marginal location in the winter may be completely unreachable come spring. Even rain and snow can cause significant disruption to microwave signals used to tie transmitter sites together or to carry data.
In addition to the natural causes, there are several structural considerations that can reduce the usefulness of firefighting communications. One of these is the density of the structure. In designing radio systems, vendors typically refer to "light," "medium" and "heavy" construction, which roughly correspond to residential, general commercial/multiple dwellings, and large industrial, mercantile and institutional structures, respectively. As firefighters, we recognize the different building materials used in these applications. But just as a wood-frame home will behave differently toward fire than will a steel and concrete high-rise, each will also exhibit a unique resistance to radio waves.
As can be expected, the lightweight home will present little barrier to the use of radios in a properly designed communications system, but not all residences fall into the lightweight category. In fact, some that may normally not be considered as substantial can create problems. Tests conducted on National Weather Radio signals in Florida found that mobile homes and steel studs significantly hamper proper reception. This is bad news for any department using high-band VHF equipment, which is essentially the same spectrum utilized by the National Weather Service.
Almost any significant use of metal building materials - including aluminum and steel siding - can have a negative effect. It stands to reason, therefore, that larger buildings that employ a large amount of steel framing will also be poor locations for radio reception. Here, too, other factors may also come into play. Just as water flow degrades over distance, so do radio waves. A building that contains significant floor space and has numerous walls and partitions may exhibit interior dead spots. Even office furniture, such as metal desks and filing cabinets, as well as store fixtures and machinery can all help to diminish the signal.